Polyimide resin, which has excellent heat resistance and outstanding electrical and mechanical properties, has been used for the protecting film and insulating film of a semiconductor device. Recently, however, polybenzoxazole resin has begun to be used in state-of-the-art semiconductor devices, which has no highly polar carbonyl group derived from imide ring and thus has excellent moisture resistance reliability. Furthermore, there has been developed a photosensitive resin composition which is obtained by imparting photosensitivity to a polybenzoxazole or polyimide resin so that it is able to simplify a part of the pattern forming process and thus is effective in shortening the process and increasing yield.
Recently, there has been developed a positive photosensitive resin composition which comprises a polybenzoxazole precursor which was improved in view of safety so that it can be developed in alkaline aqueous solutions, and a diazoquinone compound as a photosensitive agent (for example, see Patent Literature 1).
Hereinafter, the production of a relief pattern with a positive photosensitive resin composition and its developing mechanism will be described. First, a coating of a positive photosensitive resin composition is formed on a substrate. The coating is exposed to actinic radiation through a mask by means of an exposure apparatus called stepper, thereby forming a portion that was exposed (hereinafter referred to as “exposed portion”) and a portion that was not exposed (hereinafter referred to as “unexposed portion”). The diazoquinone compound present in the unexposed portion is insoluble in alkaline aqueous solutions, and it is provided with resistance to alkaline aqueous solutions by the interaction with the resin. On the other hand, the diazoquinone compound present in the exposed portion causes chemical change by the action of the actinic radiation to produce carboxylic acid. As a result, the exposed portion is soluble in alkaline aqueous solutions and promotes dissolution of the resin. It is able to produce a relief pattern comprising the unexposed portion only, by dissolving and removing the exposed portion using the difference in solubility between the exposed and unexposed portions.
Conventionally, the polybenzoxazole precursor resin which is contained in a positive photosensitive resin composition forming a coating pattern, is finally cured at a high temperature of near 300° C. for dehydration and ring-closure reaction, thereby obtaining a polybenzoxazole resin with excellent heat resistance. Meanwhile, as a result of the downsizing and integration of semiconductor devices in recent years, the heat resistance of, especially, memory elements is lower than before. Accordingly, to increase yield, a polybenzoxazole precursor resin which can be cured at a lower temperature is necessary. When using such photosensitive resin compositions, their sensitivity is very important. In the case of low sensitivity, that is, when the sensitivity is poor, it takes a longer exposure time and result in a decrease in throughput.
As just described, recently, there is a strong need for the development of a photosensitive resin composition which has high sensitivity and which is highly heat resistant and reliable even when it is cured at a low temperature.
When a photosensitive resin composition is used to form a semiconductor device or display device, generally, an edge bead rinse (EBR) process is employed to wash and remove a film of unnecessary photosensitive resin composition with a solvent, the film being formed at the edge of a substrate after coating.